We propose a model community-based trial in Rhode Island (RI), aimed at avoiding or minimizing morbidity from overt maternal hypothyroidism by systematic detection and treatment, beginning at the 1st prenatal visit. This model can be superimposed on existing prenatal screening programs and is intended ultimately to replace "case-finding", which has recently been shown ineffective. Three aspects of maternal and child health are compromised when a pregnant woman is thyroid deficient: 1) the woman's own health and well-being;2) her baby's brain de- velopment;and 3) overall health of the pregnancy (e.g., fetal death, prematurity, preeclampsia). Thyroid stimulating hormone (TSH) measurement, a well accepted indicator of thyroid dysfunc- tion, will serve as the primary test for both diagnosis and monitoring. A TSH value >10 mU/L indicates overt hypothyroidism. Among the state's 14,000 annual pregnancies, 42 women (0.3%) will be overtly hypothyroid early in gestation (32 undiagnosed, and 10 under-treated). TSH values between 4.5 mU/L (98th centile) and 9.9 mU/L indicate subclinical hypothyroidism. The 240 women in this category will also receive treatment, and information will be gathered about disease progression to inform future practice. Approximately half of all RI's pregnancies are cared for by practices in Greater Providence, and TSH testing will initially be introduced, there. The research component is also within that area. Testing will subsequently be extended to the entire state. The program will be centrally managed by three units at Women and Infants Hospital, in consultation with RI's Birth Defects Program Director. Program goals are to: provide TSH testing to at least 70% of pregnant women in Greater Providence provide TSH testing to at least 50% of pregnant women elsewhere in RI test 70% of screened women by 12 weeks'gestation, and 90% by 18 weeks'gestation begin treatment in Greater Providence by 13 weeks'in 70%, and by 19 weeks'in 90% document successful treatment during pregnancy in 90% (TSH >0.1 mU/L and <2.0 mU/L) retain 95% treated women to end of pregnancy, and 90% for up to 1 year postpartum obtain pregnancy complications and birth outcomes for the entire cohort (Vital Records) Data will be collected on participation by practices and women, % of women with undiagnosed thyroid deficiency, compliance with follow-up and treatment during pregnancy and for up to one year afterwards, outcomes of their pregnancies, % of hypothyroid women with postpartum thy- roid dysfunction, % of women with subclinical hypothyroidism who remain hypothyroid one year postpartum, physician attitudes, and program costs. There is general agreement that thyroid gland function should be assessed in pregnant women. When the gland produces too little thyroid hormone (hypothyroidism), all of the woman's bodily functions slow down, and there are problems with her baby's development. Until now, physicians have identified this problem on an individual basis (case-finding), but this approach misses many of the cases. Our trial aims to replace case-finding with a routine blood test that is highly effective at detecting hypothyroidism, thereby allowing treatment to correct the deficiency. This approach can eventually be implemented throughout the United States.